1. Field of the Invention
The present invention relates to a method for selectively imparting an electroless plating catalyst on a substrate to be plated and to a cylindrical coil obtained using this method.
2. Description of the Related Art
In the past, it has been known to forming, for example, wiring on a printed circuit board by electroless plating employing means using a resist, as typically represented by an additive method.
The method of forming a pattern on a printed circuit board by the additive method called for an electroless plating reaction catalyst, for example, palladium (Pd), to be imparted to the surface of the insulating substrate, then the portions other than the conductor circuit of the substrate to be covered by a resist and the substrate covered with the resist to be immersed in an electroless plating solution, whereby electroless plating was applied on only the uncovered portions on the substrate. This additive method, however, had the problem of an extremely large number of steps and the need for complicated work, as mentioned above.
Therefore, in the past, to overcome this problem, for example, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 63-212285 or Japanese Unexamined Patent Publication (Kokai) No. 62-218580, there had been proposed the method of directly drawing the wiring on a ceramic substrate, without the use of a resist, by using the local heating effect of a laser. Explaining this method of using the local heating effect of a laser in more detail, when for example using an alumina nitride substrate, the irradiation of the laser causes a reaction of:
xe2x80x83AlNxe2x80x94Al0+xc2xdN2
and changes the substrate to the metal (here, aluminum metal as shown by Al0) at the laser-irradiated portions of the substrate. The aluminum metal obtained by this laser irradiation is, in turn, used as the nucleus for electroless plating, thereby forming a circuit.
In the above method, however, in the case of an alumina nitride substrate, for example, the substrate has to be placed in a vacuum atmosphere so as to prevent the formation of an oxide layer such as alumina (Al2O3) on the surface of the substrate, necessitating expensive, large-sized facilities such as vacuum chambers. Further, even substrates such as AlN which are relatively easily metallized by irradiation by a laser require use of a high output pulse laser (hereinafter referred to as a YAG) of a peak output of 4 kW, a pulse width of 200 ns, and a repetition of 1 kHz. In the past, since use was made of a pulse laser, it was extremely difficult to form wiring with uniform wire widths, to increase the drawing speed, etc.
Further, regarding prior art coils, for example, as shown in, for example, U.S. Pat. No. 4,903,674, there have been proposed coils etc. attached to spark plugs of internal combustion engines. These have been manufactured by the additive method or the etching method, both of which use the above-mentioned circuit forming method, i.e., the resist method, which are complicated in steps and require difficult technology for attachment of a resist on a curved surface. Therefore, as shown in Japanese Unexamined Patent Publication (Kokai) No. 63-212285 and Japanese Unexamined Patent Publication (Kokai) No. 62-218580, consideration has been given to applying electroless plating to just the laser-irradiated portions, but as mentioned above, the formation of wiring with uniform wire widths, the increase of the drawing speed, etc. end up becoming extremely difficult.
Accordingly, the objects of the present invention are to eliminate the above-mentioned disadvantages of the prior art and to provide a plating method capable of selectively imparting an electroless plating catalyst selectively to a circuit substrate etc. simply and with few steps.
Another object of the present invention is to provide a cylindrical coil obtained by selective formation of a coil wiring pattern by plating, without the use of the resist method accompanying with its complicated steps.
In accordance with the present invention, there is provided a plating method comprising:
(1) imparting an electroless plating reaction catalyst to a surface of a substrate;
(2) deactivating or removing the electroless plating reaction catalyst imparted to the substrate surface by a reaction-catalyst selective-imparting means at only desired locations of the electroless plating reaction catalyst; and
(3) applying electroless plating to the locations of the substrate having the electroless plating reaction catalyst.
In accordance with the present invention, there is also provided a cylindrical coil having a cylindrical substrate and a spiral-shaped conductor formed on at least one side surface of the substrate, obtained by imparting an electroless plating reaction catalyst on the side surface of the cylindrical substrate, then deactivating or removing the electroless plating reaction catalyst in the form of a continuous winding at the side surface of the cylindrical substrate, then causing a reaction between said electroless plating reaction catalyst and an electroless plating solution.